Using a RADES9300 and serial ethernet to connect to plc...Works over eth but not dial

bdoub1eu

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Join Date
Jul 2006
Location
Charlotte, NC
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Hi all!

First let me say that I'm a Network Administrator so I don't know alot about PLC's. I'm helping our Engineers figure out a way to do this. If my explanation doesn't sound right or is confusing, email me back and I'll try to explain better.

As you know, most PLC's are now ethernet enabled, but there are some older PLC's that are RS-232. What our engineers are trying to do and test is dialing up to a remote customer site (That has an ethernet network and Serial Ethernet Servers to convert serial to ethernet. They are currently using a RADES9300 to dial in and then the ethernet on the RADES9300 is then connected to the Ethernet Serial Server (I think it's made by blackbox...PN# LES401A) which is then connected through serial to the PLC.

There is then software that uses the ethernet connection to search for the serial interface (I guess using the serial ethernet server). Once it sees it, it will create a virtual com port connecting the laptop to the serial interface. Easy enough right?

On the LAN, this works fine and the software sees the serial port and creates the virtual com port on the laptop. The problem is that these are at remote sites and they will be using dialup. When they dial into the RADES 9300, they get an IP and can ping the Serial Ethernet Server but when the software tries to create the virtual com port, it looks at the ethernet connection on the laptop to do it. The only problem is the laptop is dialed in and nothing is connected to the ethernet port. I talked to black box and they said it won't work because when you are dialing in, you are using a modem (COM) port.

Shouldn't matter should it? Once they are connected over dialup or ethernet, they have complete network capability as far as pinging everything but they can't create the virtual com port since that particular software uses the ethernet to look for the serial interface instead of any available connection the laptop has.

They can dial in dirctly to the PLC but overall, they want to dial into a device and be on the local LAN and communicate to the PLC's with a serial ethernet converter but this doesn't seem to be working over dialup.

Has anyone experienced anything similar? Thanks in advance!
 
I understand what you are trying to accomplish as I have done this on a few occassions also. For most of them I have VPN access to the remote site and did not need to use dial up. We do have one site that has a modem line as back up just in case the VPN is down. I just tried it and I was able to connect to my PLC through the Ethernet/Serial server. I am using a Moxa Nport model 5110 server. I am dialing into a DB server running Windows Server 2003 with a modem attached to it. I don't understand the statement from Blackbox about it not working because the modem is using a com port. As long as the modem is not configured as the same com port as the Ethernet server it should work OK. You can access more than one com port at a time, just can't have multiple applications use the same com port
 
I got lost at the part about the "software that uses the ethernet connection to search for the serial server".

This software is supplied by the serial server vendor? It resides on the PC which is attempting dial-in and connection to the serial server?

"On the LAN this works". Do you mean you test the serial server on your LAN accessing some serial device; where the laptop is connected to the LAN via ethernet but the 9300 is not part of the test, correct?

It sounds like when you attempt to use the 9300, you cannot "point" the software seeking the serial server at the laptop COM port, that the software defaults to the ethernet port.

When using the 9300 can you dial-in and access devices on the LAN other than the serial server?

Dan
 
It seems highly unlikely, but black box might be relying on raw level 2 ethernet framing to talk to the device instead of more traditional transport layer approaches like UDP/TCP... or maybe their software is just crappy and defaults to the ethernet adapter.

I've been pretty happy with MOXA, but I've never used it's virtual com port stuff with dial-in. It sounds like MHennel has had some success with this though.

EDIT: I just looked up the serial server you are using and noticed that it's using Vlinx for management. This is the same software that MOXA uses for the Nport Serial Servers we use. If you set the IP address of the serial server static, you should be able to 'find' the server by searching by it's IP address instead of using the automatic discovery.
 
Last edited:
Here is what I am thinking:

When your dial connection established your computer creates TCP/IP socket (Winsock) over a dial-up connection ie virtual network adapter that has only TCP/IP transport.

When you ping remote device it goes over TCP transport and works just fine.
But when "dicovery" program from blackbox most likely not using TCP.
I don't know what they use, but most likely something non-TCP, based on MAC address range (ARP may be).
This will go over regular LAN adapter, but not over virtual dialup adapter.

Do Ethereal traffic capture on Dial-Up adapter to see what they use and yuo can bind this protocol to dial-up adapter.

Again, this is just a guess...
 
Oh and I'm confusing myself... it's B&B Electronics that uses Vlinx, not MOXA. So yeah... pretty much ignore me, or you'll just get sucked into my web of confusion.
 

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